Pro-inflammatory mediators produced in response to Plasmodium falciparum infection contribute to severe malaria. However, very little is known about the mechanism by which these immune responses are elicited and are regulated. The glycosylphosphatidylinositols (GPIs) have been proposed as the major parasite factors that contribute to malaria pathogenesis. Previously, we showed that GPI-induced activation of macrophages is mediated mainly by TLR2 via the activation of the MyD88-dependent MAPK and NF-KB pathways, which differentially contribute to the production of pro-inflammatory mediators. Since GPIs are membrane bound and are not released during schizont burst, which produces peak levels of pro-inflammatory responses, it is important to study the physiologically relevant parasite components that are the targets of the immune system with regard to the host receptor specificity and receptor-dependent modulation of innate immune responses. Further, little or no information is available on the receptor specificity in the recognition of parasites by dendritic cells (DCs), which play crucial role in the initiation and modulation of innate immunity. Extending the work done during the previous grant period, we propose the following Specific Aims: (1) To study the mechanism of ERK-dependent dysregulation of GPI-induced IL-6 and IL-12 production and to investigate the requirement of TLR1 or TLR6 for recognition of GPIs.(2) To investigate the receptor specificity in the pro-inflammatory responses to parasite schizont-released components in macrophages and DCs, and activation of T cell responses by DCs. (3) To determine in vivo whether the receptor specificity of P. berghei mirrors the ligand-receptor specificity observed for the major TLR ligands of P. falciparum. (4) To study the malaria parasite-induced tolerance with regard to switching from pro- to anti-inflammatory responses by macrophages and DCs, and the modulation of T cell responses by DCs. The overall goal is to gain in-depth understanding of the mechanisms of cell signaling and regulation of innate immune responses to malaria parasite. The long-term objectives of this project are to understand in detail the mechanisms of innate immune responses to P. falciparum infection and to use this knowledge for therapeutic benefit. Malaria is a major public health crisis around the world, affecting ~40% of the population and killing 2- 3 million people annually. Currently, malaria is spreading rapidly due to drug resistance. A large number of people from non-malaria regions (military and business personnel, diplomats and visitors) are also at increased risk and are particularly more vulnerable to severe or even fatal forms of the disease because of their non-immune status. Therefore, novel drugs/therapeutic and/or vaccine are needed urgently. The knowledge gained by the studies proposed in this application should prove valuable in combating malaria.